Does anyone have experience adjusting the two proportioning valves on the rear brake lines under a 142 (I think I've seen them on 120's also) ?

I would like to increase the line pressure to the rear brakes for more rear bias.

Which way do I turn the screw? How sensitive is the adjustment? IE how many degrees of rotation will net how much effect? (approximately)

Any chance these near 50 year old buggers will just self destruct when I turn the adjuster? I'll be eventually converting to a single line and a wilwood proportioning valve, so I can hold off. But it would be nice to dial in the brakes a little better in the interim.